1. Field of Invention
The present invention relates to a method of assembling an electrical junction box suitable to be connected for example to a wire harness in a vehicle such as an automobile.
2. Description of Related Art
Recently, the increase of electrical and electronic component parts which are mounted in a vehicle has led to increase of circuits to be accommodated in electrical connection boxes and junction boxes in the vehicle. Thus, when forming branch circuits at a high density, it is necessary to mount a large number of component parts on a junction box or the like, which causes increase of manufacturing complexity.
In a junction box disclosed in JP-A-2000-92660 and shown in present FIG. 10, bus bars 5A-5D are laminated one upon another between an upper case part 2 and a lower case part 3, with insulation plates 4A-4E interposed between the bus bars 5A-5D. The upper case part 2 has a connector receiving portion 2a, a relay receiving portion 2b and a fuse receiving portion 2c, on which in use connectors 6, relays 7 and fuses 8 are mounted respectively. Terminals of the connectors 6, the relays 7 and the fuses 8 are connected to tabs 5a projecting from the bus bars directly or are connected to the bus bars through relaying terminals. The lower case part 3 has also a connector receiving portion 3a to connect connectors to tabs projecting from the bus bars.
In the junction box 1, with the increase of the number of circuits, the area and the number of layers of the bus bars increase and thus the size of the junction box becomes large. If the connector, relay and fuse receiving portions are arranged on both the upper and lower case parts to connect connectors, relays and fuses to internal circuits of the junction box, it is possible to make the area of the junction box smaller than in the case where the receiving portions are mounted on only the upper case part or the lower case part.
However, if the connector, relay and fuse receiving portions are mounted on both the upper and lower case parts such that they are opposed vertically, the bent tabs of bus bars must overlap each other and thus cannot be easily arranged. In this case, it is necessary to form tabs on bus bars of other layers, which causes an increase of number of layers of bus bars, and thus leads to the increase of the height of the junction box. That is, the junction box is necessarily large.
Further, the above-described junction box is so constructed that the bus bars are connected to the connectors, the fuses and the relays. Thus, when the specification of the connection between the internal circuit and the fuses and/or the relays is altered, it is necessary to alter the entire internal circuit. Consequently the above-described junction box is incapable of allowing a circuit alteration easily.
Some proposals have been made for replaceable modules in electrical circuits of automobiles.
U.S. Pat. No. 5,179,503 shows a modular automobile power distribution box having replaceable modules carrying relays or fuses. The relays or fuses in each module are directly connected to terminals of leads of wire harnesses. A pair of bus bars connect power terminals to the fuses of three maxi-fuse modules. There is no discussion of interconnection of the modules.
U.S. Pat. No. 5,581,130 discloses removable multi-function modules in individual casings which are mounted on a circuit board. Each module is electrically connected to the power supply distribution layer of the board by a pin. Alternatively three modules are shown connected together by two electrical and mechanical coupling bars.
It is an object of the present invention to provide a method of assembling a junction box which can be made thin without increasing the number of layers of bus bars to be accommodated therein and which can cope with a circuit alteration easily.
According to the present invention, there is provided a method of assembling an electrical junction box adapted to provide electrical connection to a plurality of electrical connectors, a plurality of fuses and a plurality of relays. The method includes:
(i) assembling in a casing the following components:
(a) a connector circuit having at least one connector circuit insulation substrate having opposite main surfaces and a periphery around the main surfaces, a plurality of first bus bars fixed on the insulation substrate, the first bus bars being arranged to provide electrical connection to electrical connectors in use and having at least one first welding portion at an end of one of the first bus bars and standing up from one of the main surfaces and at least one second welding portion formed at an end of one of the first bus bars and extending laterally from the periphery of the insulation substrate;
(b) a fuse circuit having at least one fuse circuit insulation substrate, which is discrete from the connector circuit, and a plurality of second bus bars fixed on the fuse circuit insulation substrate, the second bus bars being arranged to provide electrical connection to fuses in use; and
(c) a relay circuit having at least one relay circuit insulation substrate, which is discrete from the connector circuit, and a plurality of third bus bars fixed on the relay circuit insulation substrate, the third bus bars being arranged to provide electrical connection to relays in use;
at least one of the fuse circuit and the relay circuit having a third welding portion at an end of a bus bar thereof and upstanding away from the insulation substrate thereof and a fourth welding portion at an end of a bus bar thereof and extending laterally from the insulation substrate thereof;
the assembling step including the steps of:
(ii) joining the first and third welding portions to form a welded connection by arranging them lying adjacent each other and welding them together; and
(iii) after step (ii), joining the second and fourth welding portions to form a welded connection by welding them together when superimposed one on the other.
The present invention also provides a junction box assembled by the above-described method.
The electrical junction box of the present invention has a modular construction. As described above, in the junction box of the present invention, the fuse circuit substrate and the relay circuit substrate are separately provided from the connector circuit substrate and are then joined by welding of the welding portions.
A connector module, which includes the connector circuit, has a welding portion formed by vertically projecting the end of the bus bar from the upper surface of the insulation substrate and a welding portion projected horizontally from the periphery of the insulation substrate. A fuse module and/or a relay module to be connected to the connector module respectively include the fuse circuit and the relay circuit, and have a welding portion formed by projecting an end of a bus bar from the periphery of an insulation substrate at one side thereof and bending it perpendicularly, i.e., vertically away from the insulation substrate. The fuse and/or relay module also have a welding portion formed by horizontally projecting the end of a bus bar from the periphery of the insulation substrate at the other side thereof.
The fuse module and/or the relay module are disposed at a predetermined position relative to the connector module by superimposing them on each other. The bus bars of the connector module and those of the fuse module and/or the relay module are connected to each other by superimposing and welding the corresponding vertical welding portions to each other and the corresponding horizontal welding portions to each other.
In the junction box of the present invention, the connector module, the fuse module and the relay module are separately formed by separately providing the connector connection circuit to be connected to external wires through a connector, the fuse circuit and the relay circuit. That is, the connector connection circuit bus bars, the fuse connection bus bars, and the relay connection bus bars are separately provided.
Alternatively, as described below, the fuse circuit and the relay circuit may be integrated.
In contrast, in the conventional method, in which electrically conductive sheets are punched to form unitarily the connector connection circuit, the fuse connection circuit and the relay connection circuit and form tabs to be connected to connectors, tabs to be connected to fuses, and tabs to be connected to relays and stacked in a single stack, the circuits thus being handled and arranged in a complicated manner. Consequently, in the conventional method, the area of the bus bars increases and a large number of bus bars are necessary.
On the other hand, in the present invention, because the circuits are separately provided and welded to join them, it is possible to avoid the complication of tabs overlapping each other and avoid a large number of bus bars. Thus, it is possible to form a thin or compact junction box. Further, because the circuits of the bus bars can be handled and arranged easily, the area of each bus bar can be reduced. Consequently, even though the bus bars are separately provided for the connector connections on the one hand and the fuse connections and the relay connections on the other hand, it is possible to reduce the total area of the bus bars and avoid increase of the area of the junction box.
Further, the connector module having the connector circuit, the fuse module having the fuse circuit and the relay module having the relay circuit are all separately provided, i.e., the respective insulation substrates are discrete from each other. Thus, if any one of the specification of the connector circuit, the fuse circuit, and the relay circuit is altered, only the design of any one of the modules need be changed. That is, the construction can cope with the alteration of the specification easily.
The fuse module and/or the relay module are for example located at a predetermined position relative to the connector module by superimposing the fuse module and/or the relay module on the connector module. The bus bars are connected to each other by welding the upstanding welding portions to each other and the lateral welding portions to each other. The connector connection bus bar is provided separately from the fuse connection bus bar or/and the relay connection bus bar but connected thereto by welding. Thus the construction does not reduce reliability of the electrical connections. The welding portions are superimposed on each other and connected to each other by ultrasonic welding, resistance welding, laser welding or gas welding.
Typically, when welding the welding portions formed at the ends of the bus bars, a welding portion formed at an end of one bus bar, and, for example, projecting at a periphery of the fuse module and/or the relay module, and bent upward, is arranged alongside and welded to a welding portion of an end of another bus bar projecting upward from an upper surface of the insulation member of the connector module. Thereafter a welding portion formed at an end of a bus bar, e.g., projecting laterally from a periphery of the fuse module and/or the relay module, is superimposed with and welded to a welding portion of an end of a bus bar projecting laterally from the periphery of the connector module. Thereby the connector module and the fuse module and/or the relay module are connected to each other. Thus, initially, the welding portions perpendicular to the insulation substrates of the connector module and the fuse module and/or the relay module are welded to each other. Thus, even though the position of the insulation substrate of the fuse module and/or the relay module is dislocated horizontally relative to the insulation substrate of the connector module owing to deformation of the bus bars caused by thermal expansion or shrinkage or compression caused by mechanical deformation thereof, such dislocation can be permitted. This is because the laterally projecting welding portions are superimposed on each other in such a way that their main surfaces are parallel with the dislocation direction of the insulation substrate of the fuse module and/or the relay module. Accordingly, it is possible to smoothly weld the laterally projecting welding portions to each other in a subsequent welding process. Further, there is no possibility that a large stress remains in the welding portions.
Although the fuse circuit and the relay circuit may be separately formed, it is possible to integrate them with each other to form a fuse/relay composite circuit which receives fuses and relays on the same substrate which has bus bars for fuses and relays on it. In this case, if it is necessary to connect the circuit of any of the bus bars for fuses to any of the bus bars for relays, the respective bus bars may be welded to each other, or the bus bars may be integrally formed.